Asuncion in January and February
I was in Asuncion during both January and February this year. The average temperature was 45 deg see with 80% humidity. This was interspaced by torrential rainfall periods.
I am 56, 187 cm tall, caucasian, about 15kg overweight and I found it debilitating. I would attend Spanish school in the morning then retreat to my hotel room until about 5pm when it cooled off enough to go outside. I hired a car for 3 weeks, both to get around, and because travelling in unairconditioned taxis or colectivos was sickening.
Infierno is a true assessment.
I am going back because I love the place, but between April and November. I was also there during March and you could feel the difference. The days were still in the high 30's but the humidity dropped off a bit and it was bearable, approaching nice.